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STL question

Started by gumpy Apr 5, 2005 at 8:00 AM 4 replies 1.1k views

Original Post

Apr 5, 2005 at 8:00 AM

i'm hoping this is the proper place for this thread. after seeing boolean's thread the other day on "worst hello world" i decided to use that idea to become more familiar with stl. in this example, i was looking for a solution to using for_each without having to declare the data type of the contents of the container. the only thing i could get to work is this structure.


#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
struct f{
    template<typename T>
    void operator()(T&t){std::cout<<static_cast<char>(t);}
};
int main() {
    std::string s("Hello World!");
    std::vector<int>v(s.begin(),s.end());
    for_each(v.begin(),v.end(),f());
    return 0;
}

i was wondering if this is only or proper way to do this.

Telastyn

Apr 5, 2005 at 11:01 AM

#include <string>#include <iostream>#include <vector>#include <algorithm>using namespace std;class   printfun{private:public:        template <typename T>        void    operator()(T t){                cout << t;        }};int main(int argc, char *argz[]){string  foo="foo: Hello world.";char    bar[]="bar: Hello world.";vector<char>    moo;moo.push_back('m');moo.push_back('o');moo.push_back('o');for_each(foo.begin(),foo.end(),printfun());cout << endl;for_each(&bar[0],&bar[strlen(bar)],printfun());cout << endl;for_each(moo.begin(),moo.end(),printfun());cout << endl;}

produces:

foo: Hello world.bar: Hello world.moo

Though mine doesn't pass by reference, simply because I'd forgotten until now...

Fruny

Apr 5, 2005 at 12:01 PM

#include <iostream>#include <string>#include <vector>#include <algorithm>#include <iterator>int main(int argc, char *argz[]){  std::string str = "Hello World.";  std::copy(str.begin(), str.end(), std::ostream_iterator<char>(std::cout, ""));  std::cout << std::endl;  std::vector<char> vec(str.begin(), str.end());  std::copy(vec.begin(), vec.end(), std::ostream_iterator<char>(std::cout, ""));  std::cout << std::endl;}

If you don't want to declare the type of the contents of the container, your solution is acceptable. Though I wouldn't bother with the static_cast - if you have a std::vector, you're going to write ints, right? If not, well, you'll have to specify the type you want to print out somehow, which brings us back into the domain covered by std::ostream_iterator. [smile]

gumpy

Apr 5, 2005 at 12:13 PM

well ya, it's a pointless example. the concept i pointed out is what i'm looking at. and ya, it works as a class as well as a struct.

Fruny

Apr 5, 2005 at 12:28 PM

Quote:
Original post by gumpy macdrunken
well ya, it's a pointless example. the concept i pointed out is what i'm looking at. and ya, it works as a class as well as a struct.

Ok, then consider something like this, which might be what you were looking for:

template<class T> struct Foo{  T m_t;  Foo(T t) : m_t(t) {}};template<class T> Foo<T> make_foo(T t){   return Foo<T>(t);}

The type T is deduced from the parameter you passed to make_foo. If you pass it an int, you get a Foo, if you pass it a std::string, you get a Foo. If you're using such a make_foo as a parameter to a function template (e.g. for_each or copy), you never need to explicitely refer to Foo<whatever>.

That's how std::make_pair, std::bind1st, std::bind2nd, std::mem_fun, std::mem_fun_ref, std::ptr_fun ... work.

Jingo

Apr 5, 2005 at 12:48 PM

Prefer std::ostreambuf_iterator :)

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